In fluid devices such as spool valves or directional control valves, as well as piston-cylinder devices, it is often desirable to detect the position of a spool, piston or similar in order to ensure proper operation of the fluid device. A conventional sensor used for this purpose is a magnetic sensor, commonly referred to as a Hall sensor.
U.S. Pat. No. 6,283,149 discloses a sensor arrangement for a directional control valve, where a magnetic sensor is mounted in a blind bore in the valve body. Magnets are provided in an outer radial surface of the spool, which magnets are used by the sensor for determining the position of the spool. This arrangement requires the sensor to detect a magnet through a section of the wall, which may reduce the accuracy of the sensor. The solution also requires additional machining of both the valve body, to allow mounting of the sensor, and the spool, to allow magnets to be mounted on the spool. This makes the manufacture of the valve unnecessarily complex and expensive.
WO 2007/076750 discloses an alternative arrangement for mounting a sensor. In this example, the sensor is mounted in a bore exiting in a cavity for a spool in a valve body. The sensor uses magnets mounted on a projection on the spool to detect the position thereof. This arrangement exposes the sensor to the hydraulic fluid in the cavity, which may cause the sensor to corrode and eventually malfunction. This solution also requires additional machining of the spool, to allow magnets to be mounted on the spool.
One object of the present invention is to provide an improved arrangement for detecting the position of a displaceable component in a fluid device, which arrangement solves the problems stated above. The invention aims to provide a sensor arrangement having an improved accuracy and which is less affected by hydraulic fluid.